1. Field of the Invention
The present invention relates to a cellulose ester film and a method for manufacturing the same. In more detail, the invention relates to a cellulose acylate film which contains a cellulose acylate and has a large Rth per film thickness and in which when processed into a polarizing plate and then stuck to a panel, its display becomes uniform within a plane, and a method for manufacturing the same. The invention also relates to a polarizing plate and a liquid crystal display device each using the cellulose acylate film.
2. Description of the Related Art
In liquid crystal display devices of recent years, slimming has been advanced, and a trend toward this is conspicuous especially in liquid crystal display devices for television in which high added values such as high definition and large screen are required.
In response thereto, slimming of respective constitutional parts is required. In particular, for members in a film form, such as polarizing plates and optically compensatory films, optical films satisfying the requirement for slimming and simultaneously having suitable optical performance and mechanical physical properties are demanded.
Also, in designing the optical performance, in addition to the trend toward slimming by complexation of functions of an optical film such as adoption of a biaxial film, for the purposes of ensuring robustness against a performance fluctuation by the environment and ensuring stiffness, lamination of a uniaxial film such as a so-called A-plate having a retardation only in an in-plane direction and a so-called C-plate having a retardation only in a thickness direction is also studied. It may be considered that a necessity for uniaxial films having high versatility, and in particular, in the case of considering slimming, a C-plate having a retardation only in a thickness direction, will increase.
As for a relation between optical function and elastic modulus, for example, JP-A-2008-058893 describes an increase of the elastic modulus in a stretching direction by stretching a cellulose film. However, in that case, a retardation is generated in the stretching direction, (that is, Re which is in plane retardation increases) so that though the elastic modulus can be ensured, the film becomes a biaxial film, and the technology of this patent document is not applicable to the formation of a uniaxial film, and in particular, it is unsuitable for the formation of a C-plate substantially having only retardation (Rth) in a thickness direction.